The present invention relates generally to a production system for producing so-called electromechanical products such as home electric products of VTR, etc. and OA products of printers, etc. that are composed of plastic molded parts, sheet metal pressed parts and machine processed parts as well as to a control method therefor and, more particularly, to a production system and a control method therefor that are suitable for eliminating the necessity for an automatic warehouse, an automated ground vehicle and so forth by getting rid of futility of mere movements of the parts by use of a plurality of units in which processing and assembling of the parts are integrated in accordance with products to be produced.
A typical construction of a so-called FA system is illustrated in the upper section of FIG. 1. It is a common practice for such a system that processing and assembling of parts are performed separately in different places over organizations or enterprises. The parts are processed in a part processing shop or a subcontract factory, then inspected and packed, and the thus packed parts are carried to an assembly shop. In the assembly shop, the parts are put into an automatic warehouse after undergoing acceptance inspections and taken out of the warehouse in accordance with a demand from the assembly line. The parts are carried by an automated ground vehicle or the like to an assembly station. In the assembly station, an assembly robot arrays, grasps and assembles the parts, if necessary, with the aid of visual recognition.
Corresponding to such a tendency, in the field of automation technology, industrial robots, automated ground vehicles and automatic warehouses have been developed. Developed and introduced in the sector of production management are an idea and technique of aggregating the parts in the assembly shop just in time and a variety of techniques of transferring the target parts at a high efficiency within the assembly shop. Then, they are integrated and controlled by computers, thus constituting FA (Factory Automation) and serving as a part of CIM (Computer Integrated Manufacturing).
Exemplified for introducing an injection molding machine on the assembly line is a production system constructed such that, as disclosed in Japanese Patent Laid-Open No. 2-165916, dies are circulated on a carrier line, and a plurality of molded parts necessary for a product are sequentially supplied in accordance with the assembly process via a clamping station, an injection station and an opening station. Alternatively, a system is, as disclosed in Japanese Patent Laid-Open No. 63-299897, constructed such that a plurality of working dies are mounted on a rotary table which is then rotated and necessary processing is effected on a terminal of an elongate member with a single press machine capable of pressing the respective working dies moved up and down. In either system, handling of the parts is simplified by circulating the dies, but this is still separate from the assembly process. Assembling to the product requires a separate means for re-grasping the part. For this reason, there arises a problem in which a part configuration possible of automatic assembly is limited. Further, the dies form the line, and hence only the necessary parts can not be obtained at a necessary time. Besides, there exists a problem in which management works such as a die maintenance, etc. are rather complicated.
FIG. 2 shows a constructive example of parts (except purchased parts) to be assembled in the assembly line of an OA appliance. A plastic molded part, a sheet metal pressed part and a machined part are ranked in this order. In home electric products and OA products, though different depending on the products, the situation is the same. Hence, a plastic part (especially small-sized molded parts) oriented unit and a pressed part oriented unit are needed as the above-described units.
A conventional injection molding machine has such a typical structure that a heating cylinder is vertically fixed to one of movable and fixed dies, a screw rotatable and movable in the axial direction is supported or fixed therein and a hopper is supported or fixed to the opposite end of the dies (p. 2, a book entitled "Precise Injection Molding", published by Kaibundo, written by Masuzawa).
A resin is melted by a band heater attached to an outer periphery of the heating cylinder. The resin assuming a melted state in the heating cylinder is extruded and charged into the dies with an advancing motion of the screw. Further, the resin is kept under pressure by rotations of the screw, thereby forming a molded part. Besides, the screw retreats to a predetermined position for next molding while feeding the resin forwards with the rotations thereof. As a mechanism for driving and controlling the screw, there are provided an actuator for rotating the screw at a rear end of the screw and an actuator for injection, and the actuators are activated to move the screw back and forth through ball screws. Simultaneously, there is adopted a system for controlling the injection force, injection speed and injection quantity through sensors such as a pressure sensor, a pulse generator and a tacho-generator (p. 33. vol. 7, Plastic Molding Technology).
In association with take-out of the molded part, there exists a structure for taking out the molded part by catching a portion of the molded part with chucks while the fixed die moves on this side, although it is usual that the molded part is dropped down by ejecting it with an ejector after opening the dies. Both the structures are not connected directly with the product on the assembly line (p. 62, No. 2, vol. 36, National Technical Report).
As a method of feeding the resin into the heating cylinder, the pellet resin put in the hopper, which is installed at the rear portion of the heating cylinder, is dropped down into the heating cylinder and consecutively extruded in front of the screw.
Further, the injection molding machine generally does not have therein a mechanism for inspecting the molded parts. The quality thereof is checked by effecting a sampling inspection on a lot unit after molding.
It is desired that the automatic warehouse and the automated ground vehicle be made unnecessary by eliminating the process and the device by which any added values are not generated as in the case of simply moving the parts in the above-described production system. It is simultaneously desired that the production system constructed of totally simple hardware and software be actualized by simplifying the parts feed and assembly devices. Moreover, it is desirable to attain reductions both in preparation and management work incidental to a supply of the parts and also an extending the possibility of assembly automation (flexible and unshaped parts, etc.).